Condensation particle counter false count performance

ABSTRACT

Various embodiments include methods and systems for reducing false-particle counts in a water-based condensation particle counter (CPC). One embodiment of a method includes delivering water into multiple wicks used for transporting separate portions of an aerosol sample flow, with the wicks extending from a wick stand on a first end to a flow joiner on a second end, combining particles from the separate portions of the aerosol sample flow into a single aerosol stream within the flow joiner prior to transporting the combined aerosol sample stream into a particle detection chamber within the CPC, sensing an excess volume of water delivered to the wicks, collecting the excess volume of water in a collection reservoir, and after receiving a signal corresponding to the excess volume of water, draining the excess volume of water from the collection reservoir. Other methods, systems, and apparatuses are disclosed.

CLAIM OF PRIORITY

This Patent Application is a Continuation of U.S. patent applicationSer. No. 15/552,396, filed Aug. 21, 2017, which is a U.S. National-PhaseFiling under U.S.C. § 371 from International Application Serial NumberPCT/US2016/019083, filed Feb. 23, 2016, and published as WO 2016/137962Sep. 1, 2016, which claims the benefit of priority of U.S. ProvisionalPatent Application Ser. No. 62/119,558, filed Feb. 23, 2015, thedisclosures of each of which are hereby incorporated by reference intheir entireties.

BACKGROUND

Condensation Particle Counters (CPCs) have different mechanisms to drainthe working fluid out of the growth tube or wick. Most contemporary CPCsrely on gravity to drain the working fluid. However, as volumetricsample flow rates increase, any working fluid that drains in to the flowpath has a tendency to create bubbles which then grow in to largeparticles that gets detected by an optical sensor within the CPC. Sincethese counts are generated internally to the CPC and are not caused byactual particles from a monitored environment, the internally-generatedcounts are considered “false-particle counts” and will occur even whenthe particle counter is sampling clean HEPA-filtered air. Performance ofa CPC is rated by the number of false counts over a specified timeperiod. For example, a semiconductor clean room may require less thansix false counts per hour. Consequently, in general, the lower thenumber of false counts, the better the instrument. The disclosed subjectmatter discloses techniques and designs to reduce or eliminatefalse-particle counts in a CPC.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a generalized cross-sectional view of a water-basedcondensation particle counted (CPC);

FIG. 2A shows a cross-section of a water-based CPC that incorporatesmany of the false-particle count reduction embodiments disclosed herein;

FIG. 2B shows a cross-section of the water-based CPC of FIG. 2A alongsection A-A;

FIG. 2C shows a cross-section of the water-based CPC of FIG. 2A alongsection B-B;

FIG. 3A shows an isometric view of an embodiment of a combination sampleinlet/wick cartridge portion and a drain sidecar portion of FIG. 2C;

FIG. 3B shows a detailed view of the drain sidecar portion of theembodiment of FIGS. 2C and 3A; and

FIG. 4A through 4C show various views of an exemplary embodiment of awick stand of FIGS. 2A and 2B.

DETAILED DESCRIPTION

The description that follows includes illustrative examples, devices,and apparatuses that embody the disclosed subject matter. In thefollowing description, for purposes of explanation, numerous specificdetails are set forth in order to provide an understanding of variousembodiments of the inventive subject matter. It will be evident,however, to those of ordinary skill in the art that various embodimentsof the inventive subject matter may be practiced without these specificdetails. Further, well-known structures, materials, and techniques havenot been shown in detail, so as not to obscure the various illustratedembodiments.

As used herein, the term “or” may be construed in an inclusive orexclusive sense. Additionally, although various exemplary embodimentsdiscussed below focus on particular ways to reduce false-particle countsby eliminating empty water droplets or bubbles being counted as actualparticles, other embodiments consider electronic filtering techniques.However, none of these techniques needs to be applied to reducing oreliminating particle counts as a single technique. Upon reading andunderstanding the disclosure provided herein, a person of ordinary skillin the art will readily understand that various combinations of thetechniques and examples may all be applied serially or in variouscombinations. As an introduction to the subject, a few embodiments willbe described briefly and generally in the following paragraphs, and thena more detailed description, with reference to the figures, will ensue.

Reported count rates in contemporaneous water-based condensationparticle counters (CPCs) are generally not acceptable for clean roomapplications due to the false-particle count rate. Current clean roomrequirements (e.g., in the semiconductor industry) specify a stringentfalse count rate of less than six counts per hour. Various embodimentsdisclosed herein include techniques and designs that were developedspecifically to reduce or eliminate false counts caused by water bubblesor empty water droplets (e.g., detected “particles” not containing anactual particle serving as a nucleation point). Although variousembodiments are discussed separately, these separate embodiments are notintended to be considered as independent techniques or designs. Asindicated above, each of the various portions may be inter-related andeach may be used separately or in combination with other false-countparticle reduction techniques discussed herein.

In the following detailed description, reference is made to theaccompanying drawings that form a part of the false-particle reductiontechniques and in which is shown, by way of illustration, specificembodiments. Other embodiments may be utilized and, for example, variousthermodynamic, electrical, or physical changes may be made withoutdeparting from the scope of the present disclosure. The followingdetailed description is, therefore, is to be taken in an illustrativesense rather than in a limiting sense.

In general, a condensation particle counter (also known as acondensation nucleus counter) is used to detect particles in a monitoredenvironment that are too small to scatter enough light to be detected byconventional detection techniques (e.g., light scattering of a laserbeam in an optical particle counter). The small particles are grown to alarger size by condensation formed on the particle. That is, eachparticle serves as a nucleation point for the working fluid; a vapor,which is produced by the instrument's working fluid, is condensed ontothe particles to make them larger. After achieving growth of theparticle due to condensation of the working fluid vapor onto theparticle, CPCs function similarly to optical particle counters in thatthe individual droplets then pass through the focal point (or line) of alaser beam, producing a flash of light in the form of scattered light.Each light flash is counted as one particle. The science of condensationparticle counters, and the complexity of the instrumentation, lies withthe technique to condense vapor onto the particles. When the vaporsurrounding the particles reaches a specific degree of supersaturation,the vapor begins to condense on the particles. The magnitude ofsupersaturation determines the minimum detectable particle size of theCPC. Generally, the supersaturation profile within the instrument istightly controlled.

While there are several methods which can be used to createcondensational growth, the most widely used technique is a continuous,laminar flow method. Continuous flow laminar CPCs have more precisetemperature control than other types of CPCs, and they have fewerparticle losses than instruments that use turbulent (mixing) flow. In alaminar flow CPC, a sample is drawn continuously through a conditionerregion which is saturated with vapor and the sample is brought tothermal equilibrium. Next, the sample is pulled into a region wherecondensation occurs. In contrast, in an alcohol-based (e.g.,(isopropanol or butanol) CPC, the conditioner region is at a warmtemperature, and the condensation region (saturator) is relativelycooler. Water has very high vapor diffusivity, so a laminar flowwater-based CPC with a cool condensation region does not workthermodynamically. In a laminar flow water-based CPC, the conditionerregion is cool, and the condensation region is relatively warmer.

Water-based CPCs have a clear set of advantages over alcohol-based CPCs.Water is non-toxic, environmentally friendly, and easy to procure. Waterhowever, also has a few disadvantages. In general, the liquid purity isnot as tightly controlled for water as for alcohols purchased fromchemical supply houses. The impurities in the water may build up in the“wick” (described below), and eventually cause the wick material tobecome ineffective. To counteract this impurity effect, distilled orhigh-purity water is frequently utilized. Additionally, the wicks areoften field replaceable by an end-user. In some environments whereextremely low particle counts are expected to be present (e.g., asemiconductor-fabrication facility), the end-user may use waterspecifically prepared and packaged for use in normal-phase liquidchromatography (NPLC). NPLC water is ultra-pure water with a lowultra-violet (UV) absorbance, often filtered through, for example, a 0.2micrometer (μm) filter, and packaged in solvent-rinsed amber glassbottles and sealed under an inert atmosphere such as nitrogen. The useof NPLC water can help to reduce or eliminate false-particle counts fromcontaminants (e.g., ions, particles or bacteria) that may ordinarily bepresent in the water.

With reference now to FIG. 1, a generalized cross-sectional view of awater-based condensation particle counter (CPC) 100 is shown. Thewater-based CPC 100 is used to monitor a particle concentration levelwithin a given environment (e.g., a semiconductor-fabrication facility).The thermodynamic considerations governing operations of water-basedCPCs is known in the art and therefore will not be discussed insignificant detail herein.

The water-based CPC 100 is shown to include a flow path 101 directing anaerosol sample flow 103 through a porous media 109. The porous media 109is also referred to as a wick and may comprise one or more various typesof hydrophilic material. The porous media 109 may comprise a continuousmaterial from the sample inlet to at or near an optical particledetector 115 (described in more detail below). Alternatively, the porousmedia 109 may comprise different sections or portions along the path ofthe aerosol sample flow 103.

In this embodiment, the porous media 109 is supplied with liquid waterfrom a water fill bottle 111 along two water-inlet paths 113. Dependingon a specific design of the water-based CPC 100, the number ofwater-inlet paths 113 may decrease to a single inlet path or the numberon inlet paths may increase. Such determinations for the actual numberof water-inlet paths 113 may be determined by a person of ordinary skillin the art based on aerosol flow rates, thermodynamics of the system,and other considerations of the water-based CPC 100. The first (closestto the sample inlet) of the water-inlet paths 113 supplies water to theporous media 109 just before a cooled conditioner portion 150 of thewater-based CPC 100. The second of the water-inlet paths 113, downstreamof the first, supplies additional water just before a heated-growthportion 170 of the water-based CPC 100. As noted in FIG. 1, smallerparticles from the sample inlet have “grown” in size due to condensationof water vapor onto the particles. Large particles have a different andgenerally larger scattering signature than small particles.Consequently, larger particles 105 with a condensation layer are nowmore readily detected by the optical particle detector 115 than thesmaller particles entering the sample inlet.

For example, the larger particles 105 in the flow path comprising theaerosol stream cross a “focus point” of a beam of light 121 emitted by alight source 117, typically a solid-state laser diode. The focus pointis formed by an optical element 119 focusing light (e.g., to adiffraction limited point or line that is generally perpendicular toboth the direction of the light beam and the aerosol flow path) outputfrom the light source 117. Scattered radiation 123 individually createdby each of the larger particles 105 is sensed by an optical detector125. The larger particles 105 continue out of the optical particledetector 115 and are either captured by a filter 129 or continue into awater separator 143. Either periodically or continuously, the waterseparator 143 is drained by a drain pump 145 to a water drain discharge147.

Overall aerosol flow through the flow path 101 is maintained by asample-flow pump 127. In the embodiment shown in FIG. 1, the aerosolflow rate is maintained by a critical orifice 131. In other embodiments,a standard orifice or other type of flow control mechanism may beemployed. Critical orifices are frequently used in gas-flow samplinginstruments as they are able to maintain a constant flow rate provided asufficient differential pressure is maintained across the orifice. Thesample-flow pump 127 may either be a pump internal to the water-basedCPC 100 or may be an externally-connected pump. In some embodiments, thewater-based CPC 100 may be connected directly to a vacuum-supply sourceplumbed within a facility (e.g., a vacuum-supply source of thesemiconductor-fabrication facility). Pump exhaust 141 is filtered priorto release to ambient air so as not to increase a contamination level ofthe monitored environment.

The sample-flow pump 127 may also provide a flow from the sample inletthrough a secondary gas-flow path that includes a transport flow filter135, a second critical orifice 137 and an optional transport flow valve139. The optional transport flow valve 139 may be used to reduce a totalgas flow rate if the differential pressure across the second criticalorifice is not sufficient to maintain a constant pressure.

Referring now to FIG. 2A, a cross-section of a water-based CPC 200 isshown and incorporates many of the false-particle count reductionembodiments disclosed herein. Additional details of the water-based CPC200 are discussed with reference to FIG. 2B (indicated by section lineA-A) and FIG. 2C (indicated by section line B-B), below. The water-basedCPC 200 functions similarly in basic operation to the water-based CPC100 of FIG. 1. Additionally, the water-based CPC 200 is shown to includea removable wick cartridge 201 that may be configured to be readilyremovable by the end-user. The removable wick cartridge 201 includes awick stand 203 that is affixed over the removable wick cartridge 201 anda conical section 205. Adjacent to the removable wick cartridge 201 is adrain sidecar 207 having a drain reservoir 209 formed therein.

A sample inlet (shown and described in more detail with reference toFIG. 2B below) is located near a lower edge of the removable wickcartridge 201. Particles contained within an aerosol stream arrivingthrough the sample inlet traverse a flow path 213 through one or morewicks 211. In the various views shown by FIGS. 2A through 4C, threewicks are used to form the flow paths 213. However, this number may bechanged depending on factors related to maintaining a sufficiently lowReynolds number to maintain a laminar flow of the aerosol stream throughthe one or more flow paths 213. Such factors are known to a skilledartisan and include determining a ratio of inertial forces to viscousforces of the aerosol flow based on a mean velocity and density of thefluid in the aerosol stream, as well as dynamic and kinematicviscosities of the fluid, and a characteristic linear dimension relatingto an internal cross-section of the wicks. Additionally, a single wickwith multiple paths formed therein (e.g., by drilling out the paths) mayalso be used.

The wick stand 203 splits the incoming aerosol stream and contains anumber of outlet paths equal to the number of wicks. In the embodiment,depicted by FIG. 2A, the wick stand 203 has three outlet paths. Asdescribed in more detail with reference to FIG. 4A through FIG. 4C, thewick stand also provides a physical mechanical-interface onto which thewicks 211 are mounted. When more than one wick is used, a flow joiner215 combines particles from the three aerosol streams into a singleaerosol stream immediately prior to a particle detection chamber 219.The particle detection chamber may be similar to the optical particledetector 115 of FIG. 1.

One or more cooling fans 223 reduce or eliminate any excess heatproduced within the water-based CPC 200 by, for example, one or morecircuit boards 221, as well as heating elements and thermo-electricdevices, as discussed in more detail below.

Similar to the basic thermodynamic principles discussed with referenceto the CPC of FIG. 1, the water-based CPC 200 of FIG. 2A shows aconditioner portion 220, an initiator portion 240, and a moderatorportion 260. The conditioner portion 220 is cooled to begin the processof forming a condensate on particles in the aerosol stream. Theinitiator portion 240 is heated and is the portion of the water-basedCPC 200 where condensate is formed on each of the individual particles.The moderator portion 260 is cooled sufficiently, relative to theinitiator portion 240, such that moist air entering the particledetection chamber 219 is reduced or eliminated. A water fill bottle 217provides a reservoir of clean water (e.g., NPLC, other ultra-pure water,or distilled water) to keep the wicks 211 hydrated to provide watervapor in the flow path 213 to condense on the particles. However, eitheran excess volume of water, or water provided to the wicks 211 toorapidly (e.g., when supplied in “spurts”), can contribute to theformation of either water bubbles or empty droplets not containing anyparticles. Either of these conditions can lead to an increase infalse-particle counts.

In one embodiment, water from the water fill bottle 217 is supplied tothe wicks 211 by gravity feed. In another embodiment, water from thewater fill bottle 217 is supplied to the wicks 211 periodically throughwater pumps (described with reference to FIG. 2B, below). In anotherembodiment, water from the water fill bottle 217 is supplied to thewicks 211 either continuously or periodically through asyringe-injection arrangement (not shown specifically but understood bya skilled artisan). In another embodiment, the water fill bottle may beeither slightly pressurized or driven with a pneumatic or hydraulic ramsystem to act as a type of syringe-injection system. In anotherembodiment, water from the water fill bottle 217 is supplied to thewicks 211 periodically from either the water pumps or one of the typesof syringe-injection system through a pulsation damper (e.g., areservoir designed to reduce or eliminate rapid increase in volumetricflow of the water). By supplying the water either continuously (e.g.,through syringe-injection) or periodically (e.g., utilizing thepulsation damper mechanism), excess water over a short period of time tothe wicks is reduced or eliminated. In various embodiments, hydrogenperoxide may be added to the water fill bottle 217 to prevent bacterialgrowth. In various embodiments, silver impregnation of the wicks orother bio-inhibitors may be employed either separately from or incombination with hydrogen peroxide added to the water fill bottle. Likeparticles in the aerosol stream, bacteria formed within the water can bethe basis of a nucleation point in the flow path 213. Condensed water onthe bacteria flowing into the particle detection chamber 219 will thenbe counted as a particle. The bacteria therefore can also increase thefalse-particle count of the CPC.

Referring now to FIG. 2B, a cross-section 230 of the water-based CPC 200along section A-A of FIG. 2A is shown. The cross-section 230 moreclearly indicates both the sample inlet 231 and a flow-splitterarrangement 233 as discussed with reference to FIG. 2A above. Thecross-section 230 is also shown to include thermo-electric devices 235thermally coupled to each of the conditioner portion 220 and themoderator portion 260, heating elements 237 thermally coupled to theinitiator portion 240, and a heat sink 239 in thermal communication withthe cooling fans 223. Also shown are a secondary circuit board 241 and anumber of water pumps 243.

With continuing reference to FIG. 2B, the conical section 205 of theremovable wick cartridge 201 is in thermal contact with theflow-splitter arrangement. In various embodiments, the conical section205 may be heated to compensate for differences in the relative humidityof a monitored environment. Although not shown specifically, the ambienttemperature and the dew-point temperature may be determined byappropriate temperature-measurement devices. Alternatively or inaddition, a humidity sensor may be used to determine relative humidityof the monitored environment. In various other embodiments, both inletand outlet dew points may be monitored. In all cases, heating theconical section 205 may reduce or eliminate effects from varying levelsof relative humidity that cause bubbles or empty water droplets to formdue to elevated levels of relative humidity.

With reference to FIG. 2C, a cross-section 250 of the water-based CPC200 along section B-B of FIG. 2A is shown. The cross-section 250 showsan exemplary location of a combination sample inlet/wick cartridgeportion 280 and a detailed view 290 of the drain sidecar 207 portion.However, the portions may be located in other areas with regard to thewater-based CPC 200. The exemplary location shown is merely provided forease of understanding the disclosed subject matter. Each of thecombination sample inlet/wick cartridge portion 280 and the detailedview 290 of the drain sidecar 207 portion was discussed briefly abovewith reference to FIG. 2A.

FIG. 3A shows an isometric view of the combination sample inlet/wickcartridge portion 280 and FIG. 3B shows the detailed view 290 of thedrain sidecar 207 portion. As shown, the wicks 211 are mountedvertically in the wick stand 203 and are surrounded by a water reservoir281. Although generally, the water reservoir collects excess water fromthe wicks 211, in various embodiments, the wicks 211 may be suppliedwith water from the water reservoir 281 or may be supplied bywater-inlet paths 113 as shown in FIG. 1. In other embodiments, acombination of both the water reservoir 281 and the water-inlet paths113 may supply water to the wicks 211. In still other embodiments, thewater-inlet path 113 may only supply water to the wicks 211 at theinitiator portion 240, or the moderator portion 260, but not both. Thislatter embodiment may be coupled with a supply of water to the wicks atthe water reservoir 281. In still other embodiments, water may only besupplied to the wicks 211 at either the initiator portion 240, or themoderator portion 260, but not to the water reservoir 281. In thisembodiment, the water reservoir 281 serves to capture excess water to bedelivered to the drain sidecar 207. Generally, regardless of the waterdelivery technique chosen, air bubbles in delivery lines to the wicks211 should be avoided to reduce or eliminate water bubbles being formedwithin the flow path 213 (see FIGS. 2A and 2B). Also, any dead airvolumes within the water delivery paths are avoided.

However, regardless of how the water is supplied to the wicks 211, anyexcess water should be drained off before it causes bubbles or emptywater droplets in the aerosol stream flowing through the flow path 213(see FIG. 2A and FIG. 2B). The drain sidecar 207, discussed brieflyabove with reference to FIG. 2A, is shown to include an exhaust-air port283, a water-sensor port 285, and a water-drain port 287. Theexhaust-air port 283 allows water from the water reservoir 281 to drainmore readily by drawing air and may be coupled to, for example, thesample-flow pump 127 (FIG. 1) or another pump mounted either internal toor external to the water-based CPC 200.

Referring now to FIG. 3B, a detailed view 290 of the drain sidecar 207portion is shown including the water-sensor port 285 includes a watersensor 291. When water is supplied to the wicks 211, excess water fromthe wicks 211 drains into the water reservoir 281. When the water supplyto the wicks 211 is sufficient, the water sensor 291 then supplies asignal to stop the water supply. The water sensor 291 may beelectrically coupled by an electrical lead to one of the circuit boards221, 241 (FIGS. 2A and 2B, respectively) to determine when water ispresent in the drain sidecar 207. A constant air flow through theexhaust-air port 283 pulls water from the water reservoir 281 toward thedrain sidecar 207. The drain sidecar 207 includes the water sensor 291that detects when the drain fills with water to a certain predeterminedlevel, at which point the water is extracted by a separate pump (notshown in FIG. 3B).

In other embodiments, the water sensor may instead comprise atemperature sensing device (e.g., a thermocouple or thermistor) or ahumidity sensing device to determine when water is present in the drainsidecar 207. Once water is detected, the water is pumped out of thedrain sidecar 207 through the water-drain port 287 by, for example, asolenoid-activated micro-pump. In a specific exemplary embodiment, themicro-pump may draw water at a variable approximate flow rate of fromabout 50 μ-liters/minute to about 200 μ-liters/minute. In otherembodiments, the micro-pump may draw water at a substantially constantapproximate flow rate of about 150 μ-liters/minute.

FIG. 4A shows an isometric top view of the wick stand 203 describedbriefly above with reference to FIGS. 2A and 2B. The wick stand 203 isshown to provide three mechanical mounts 401, one for each of the threewicks 211. As stated above, other numbers of wicks 211, andconsequently, the number of related mechanical mounts 401, may bechosen. Each of the three mechanical mounts 401 includes an opening 403through which the aerosol stream may pass, and a number of grooves 405through which excess amounts of water in the wicks 211 may pass to thewater reservoir (FIG. 3A).

In FIG. 4B, which shows a side elevational-view of the wick stand 203,the excess water channeled through the grooves 405 drains from a firstsloped surface 407 to a second sloped surface 409 to the water reservoir281 of FIG. 3A. In various embodiments, only a single sloped surface maybe employed. Also, the sloped surface may comprise a curved top surfacerather than a single flat surface. In a specific exemplary embodiment,the first sloped surface 407 has an angle of about 15 degrees asmeasured from a horizontal plane and the second sloped surface 409 hasan angle of about 45 degrees as measured from the horizontal plane.

FIG. 4C shows a top view of the wick stand 203. Although each of thethree mechanical mounts 401 is shown to include four grooves, a skilledartisan will recognize that more or fewer grooves may be employed. Also,a size of the grooves is at least partially dependent on a size of theopening 403 and an external diameter of the mechanical mount 401 (theexternal diameter being sized to accommodate an inner diameter of aselected wick).

In various embodiments, any or all of the false-particle count reductiontechniques discussed may be coupled with a digital filtering technique.Digital filtering, in the context of CPC false-particle count reduction,is based on one or more observed phenomenon that distinguishes waterbubbles or water droplets from actual particles having condensed waterformed thereon. For example, a pulse height analyzer or an oscilloscopemay be electrically coupled to a detector in the particle detectionchamber 219. The rise time and/or the shape of a resultant pulse can beused to characterize and differentiate an actual particle from a bubbleor empty droplet. In one embodiment, an “absolute filter” (e.g., a HEPAor ULPA filter) may be placed over the sample inlet 231 so that anysignal generated by the detector is a known-false particle count and theresultant signal is therefore analyzed and characterized. These signalsmay be stored in a look-up table. In a subsequent actual use of the CPCin a monitored environment, each of the generated signals is comparedwith the saved signals in the look-up table. Any signals matching thecharacteristics of the resultant signals of the known-false particlesare automatically subtracted out of the final reported particle count.

Although specific values, ranges of values, and techniques are givenvarious parameters discussed above, these values and techniques areprovided merely to aid the person of ordinary skill in the art inunderstanding certain characteristics of the designs disclosed herein.Those of ordinary skill in the art will realize, upon reading andunderstanding the disclosure provided herein, that these values andtechniques are presented as examples only and numerous other values,ranges of values, and techniques may be employed while still benefitingfrom the novel designs discussed herein that may be employed to lowerfalse-counts in water-based CPCs. Therefore, the various illustrationsof the apparatus are intended to provide a general understanding of thestructure and design of various embodiments and are not intended toprovide a complete description of all the elements and features of theapparatus that might make use of the structures, features, and designsdescribed herein.

Many modifications and variations can be made, as will be apparent to aperson of ordinary skill in the art upon reading and understanding thedisclosure provided herein. Functionally equivalent methods and deviceswithin the scope of the disclosure, in addition to those enumeratedherein, will be apparent to a person of ordinary skill in the art fromthe foregoing descriptions. Portions and features of some embodimentsmay be included in, or substituted for, those of others. Many otherembodiments will be apparent to those of ordinary skill in the art uponreading and understanding the description provided herein. Suchmodifications and variations are intended to fall within a scope of theappended claims. The present disclosure is to be limited only by theterms of the appended claims, along with the full scope of equivalentsto which such claims are entitled. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting.

The Abstract of the Disclosure is provided to allow the reader toquickly ascertain the nature of the technical disclosure. The abstractis submitted with the understanding that it will not be used tointerpret or limit the claims. In addition, in the foregoing DetailedDescription, it may be seen that various features may be groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted aslimiting the claims. Thus, the following claims are hereby incorporatedinto the Detailed Description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. A method of reducing false-particle counts in awater-based condensation particle counter (CPC), the method comprising:delivering water into a plurality of wicks, each of the plurality ofwicks for transporting separate portions of an aerosol sample flow, theplurality of wicks extending from a wick stand on a first end of theplurality of wicks to a flow joiner on a second end of the plurality ofwicks; combining particles from the separate portions of the aerosolsample flow from the plurality of wicks into a single aerosol streamwithin the flow joiner prior to transporting the combined aerosol samplestream into a particle detection chamber within the CPC; sensing anexcess volume of water delivered to the plurality of wicks; collectingthe excess volume of water into a collection reservoir; receiving asignal corresponding to the excess volume of water in the plurality ofwicks; and after receiving the signal, draining the excess volume ofwater from the collection reservoir.
 2. The method of claim 1, furthercomprising pulling a constant air flow through an exhaust-air port todrain the excess volume of water.
 3. The method of claim 1, furthercomprising detecting when a drain is filled with water to apredetermined level.
 4. The method of claim 1, further comprisingapplying a digital filter to further reduce false-particle counts. 5.The method of claim 1, further comprising: constructing a look-up tableby storing signatures of detected signals produced by knownfalse-particles; and comparing detected particle counts with the look-uptable to subtract false-particle counts.
 6. A system to reducefalse-particle counts in a water-based condensation particle counter(CPC), the system comprising: an aerosol sample inlet configured toreceive an aerosol sample flow, the aerosol sample inlet furtherconfigured to be coupled to a sample flow pump; a wick stand fluidlycoupled to the aerosol sample inlet; a plurality of wicks in fluidcommunication with and disposed between the aerosol sample inlet and thesample pump, each of the plurality of wicks to receive water and totransport separate portions of the aerosol sample flow, the plurality ofwicks extending from the wick stand on a first end of the plurality ofwicks to a flow joiner on a second end of the plurality of wicks; theflow joiner configured to combine particles from the separate portionsof the aerosol sample flow from the plurality of wicks into a singleaerosol stream prior to transporting the combined aerosol sample streaminto a particle detection chamber within the CPC; a collection reservoirto collect an excess volume of water from the plurality of wicks; and asensor to provide a signal corresponding to the excess volume of waterin the plurality of wicks.
 7. The system of claim 6, wherein each of theplurality of wicks is formed from a porous media material with an openportion formed therethrough along a length of the wick, the open portionforming an inner diameter of respective ones of the plurality of wicksand configured to direct the separate portions of the aerosol sampleflow within the open portion of each of the plurality of wicks, theplurality of wicks being substantially parallel and adjacent to oneanother within the water-based CPC.
 8. The system of claim 6, furthercomprising a water drain port coupled to the collection reservoir toremove excess water.
 9. The system of claim 6, wherein the plurality ofwicks is field replaceable by an end-user of the CPC.
 10. The system ofclaim 6, wherein the sensor is to detect when the collection reservoiris filled with water to a predetermined level.
 11. The system of claim6, further comprising a digital filter to further reduce thefalse-particle counts.
 12. The system of claim 11, wherein the digitalfilter is to compare detected particle counts with a look-up table tosubtract false-particle counts, the look-up table including a pluralityof stored signatures of detected signals produced by knownfalse-particles.
 13. The system of claim 6, wherein each of theplurality of wicks is silver impregnated to reduce or prevent bacterialgrowth within the plurality of wicks.
 14. The system of claim 6, whereineach of the plurality of wicks is treated with a bio-inhibitor to reduceor prevent bacterial growth within the plurality of wicks.
 15. Thesystem of claim 6, further comprising a removable wick cartridge coupledto the wick stand onto which the plurality of wicks is mounted, theremovable wick cartridge configured to be heated to reduce or eliminateeffects from varying levels of relative humidity, thereby reducing oreliminating bubbles or empty water droplets due to elevated levels ofrelative humidity.
 16. A system to reduce false-particle counts in awater-based condensation particle counter (CPC), the system comprising:an aerosol sample inlet configured to receive an aerosol sample flow,the aerosol sample inlet further configured to be coupled to a sampleflow pump; a wick stand fluidly coupled to the aerosol sample inlet; asingle wick in fluid communication with and disposed between the aerosolsample inlet and the sample pump, the single wick having multipleseparate aerosol flow paths formed therethrough along a length of thesingle wick to receive water and to transport separate portions of theaerosol sample flow, the single wick being coupled to the wick stand ona first end; a flow joiner in fluid communication with the single wickon a second end of the single wick, the flow joiner being configured tocombine particles from the separate portions of the aerosol sample flowfrom the multiple separate aerosol flow paths into a single aerosolstream prior to transporting the combined aerosol sample stream into aparticle detection chamber within the CPC; and a collection reservoir tocollect the excess volume of water from the single wick.
 17. The systemof claim 16, wherein each of the multiple separate aerosol flow paths issurrounded along a length of the path by a porous media with eachcomprising an open portion being configured to direct the aerosol sampleflow therein, each of the multiple separate aerosol flow paths beingsubstantially parallel and adjacent to one another within thewater-based CPC.
 18. The system of claim 16, further comprising a sensorto make a determination whether an excess volume of water is deliveredto the single wick.
 19. The system of claim 18, wherein the sensorincludes one or more sensors selected from various types of sensorsincluding a water sensor, a temperature sensing device, and a humiditysensing device, the sensor being configured to generate a signal to stopa supply of water being delivered to the single wick.
 20. The system ofclaim 16, further comprising a water drain port coupled to thecollection reservoir to remove excess water.